Acute lymphocytic leukemia (ALL) in children less than one year of age is characterized by more organomegaly, higher WBCs, an increased incidence of CNS leukemia, a high frequency of chromosome abnormalities involving 11q23, and a poor (30%) event-free survival. Recent molecular studies have suggested mechanisms by which the 11q23 region is targeted. Moreover, gene expression studies suggest that infant ALL is not a homogeneous disease : there may be multiple causes even in infants with similar chromosome abnormalities. Therapeutically, two large multicenter trials (Interfant and Children's Oncology Group) suggest that a cure rate of 50-65% can be achieved using chemotherapy regimens that contain high dose methotrexate, etoposide and cyclophosphamide. In addition, new stem cell transplantation regimens have also showed improved outcomes for infants with ALL. Recommendations for treatment are presented based upon these new biologic and clinical findings.